vaccum leak problem
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Mountain Pass
Joined: Jun 2010
Posts: 205
Likes: 3
vaccum leak problem
I am looking into a buddys problem for him. what it is, the ac (all positions) blows out the defroster vent. you can put it in 4x4 and then the ac blows out the vents like it should do but only for a couple of seconds, then returns to the defroster. The driver hub wont lock in all the time but does sometimes. From what i am reading on a couple of different post on here is it may be a vaccum leak or the hub pulse solinoid. The vaccum pump NEVER stops until you kill the truck. any ideas would be a great help.
2005, F-350 spduty, 4x4 ESOF, auto.
2005, F-350 spduty, 4x4 ESOF, auto.
Senior User
Joined: Feb 2009
Posts: 320
Likes: 2
From: Stacy, MN
The default for lack of vacuum is defrost mode. There is a vacuum leak somewhere. Try to find a cracked hose or see if there is a leak in the hubs. There are other areas to look into but start with those first. Some people (including myself) just converted to WARN manual hubs and plug the vacuum lines that go to hubs.......
Elder User
Joined: Nov 2004
Posts: 684
Likes: 1
you should see a vacuum line going from the engine compartment through the firewall and into the cab, follow it back to the source, and manually apply vacuum. then follow the line listening for leaks, and as you go along, you will find spots where it splits, clamp off the splits one at a time, when you clamp a line off, and it stops leaking, then that "CIRCUIT" is where your leak is.
This is just like tracking down a short circuit.
Good luck
This is just like tracking down a short circuit.
Good luck
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Mountain Pass
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Thread Starter
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Mountain Pass
Joined: Jun 2010
Posts: 205
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we have traced all the vacuum lines and cant find a leak anywhere. so we have decided that even though it is a 100+ right now the defrost ac is better than the old way of rolling down the windows. If anyone can give me some help i would be most thankful.
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
You clearly have a vacuum leak somewhere. You need to start at the vacuum pump. Take the line off of the nipple on the pump and put your finger over it. The pump should stop. If it does, then it is OK.
Then put that line on and move to the other end of it. Do the same thing. The pump may take a little longer to stop but it should eventually.
Keep doing this, down the line, one line and connector at a time. Eventually you will find a place where the pump never stops running. At that point you have isolated your leak.
Then put that line on and move to the other end of it. Do the same thing. The pump may take a little longer to stop but it should eventually.
Keep doing this, down the line, one line and connector at a time. Eventually you will find a place where the pump never stops running. At that point you have isolated your leak.
